in-vitro-vivo-detection-mitophagy-human-cells-c-elegans

In Vitro and In Vivo Detection of Mitophagy in Human Cells, C. Elegans, and Mice

Mitochondria are the powerhouses of cells and produce cellular energy in the form of ATP. Mitochondrial dysfunction contributes to biological aging and a ...

National Institutes of Health

University of Oslo and Akershus University Hospital

Cockayne syndrome (CS) is an accelerated aging disorder characterized by progressive neurodegeneration caused by mutations in genes encoding the DNA repair proteins CS group A or B (CSA or CSB). Since dietary interventions can alter neurodegenerative processes, Csb(m/m) mice were given a high-fat, caloric-restricted, or resveratrol-supplemented diet. High-fat feeding rescued the metabolic, transcriptomic, and behavioral phenotypes of Csb(m/m) mice. Furthermore, premature aging in CS mice, nematodes, and human cells results from aberrant PARP activation due to deficient DNA repair leading to decreased SIRT1 activity and mitochondrial dysfunction. Notably, β-hydroxybutyrate levels are increased by the high-fat diet, and β-hydroxybutyrate, PARP inhibition, or NAD(+) supplementation can activate SIRT1 and rescue CS-associated phenotypes. Mechanistically, CSB can displace activated PARP1 from damaged DNA to limit its activity. This study connects two emerging longevity metabolites, β-hydroxybutyrate and NAD(+), through the deacetylase SIRT1 and suggests possible interventions for CS.

A high-fat diet and NAD(+) activate Sirt1 to rescue premature aging in cockayne syndrome.

Mitochondria are the oxygen-consuming power plants of cells. They provide a critical milieu for the synthesis of many essential molecules and allow for highly efficient energy production through oxidative phosphorylation. The use of oxygen is, however, a double-edged sword that on the one hand supplies ATP for cellular survival, and on the other leads to the formation of damaging reactive oxygen species (ROS). Different quality control pathways maintain mitochondria function including mitochondrial DNA (mtDNA) replication and repair, fusion-fission dynamics, free radical scavenging, and mitophagy. Further, failure of these pathways may lead to human disease. We review these pathways and propose a strategy towards a treatment for these often untreatable disorders.

Protecting the mitochondrial powerhouse.

The antimicrobial peptide cathelicidin is critical for protection against different kinds of microbial infection. This study sought to elucidate the protective action of cathelicidin against Helicobacter pylori infection and its associated gastritis. Exogenous cathelicidin was found to inhibit H. pylori growth, destroy the bacteria biofilm, and induce morphological alterations in H. pylori membrane. Additionally, knockdown of endogenous cathelicidin in human gastric epithelial HFE-145 cells markedly increased the intracellular survival of H. pylori. Consistently, cathelicidin knockout mice exhibited stronger H. pylori colonization, higher expression of proinflammatory cytokines IL-6, IL-1β, and ICAM1, and lower expression of the anti-inflammatory cytokine IL-10 in the gastric mucosa upon H. pylori infection. In wild-type mice, H. pylori infection also stimulated gastric epithelium-derived cathelicidin production. Importantly, pretreatment with bioengineered Lactococcus lactis that actively secretes cathelicidin significantly increased mucosal cathelicidin levels and reduced H. pylori infection and the associated inflammation. Moreover, cathelicidin strengthened the barrier function of gastric mucosa by stimulating mucus synthesis. Collectively, these findings indicate that cathelicidin plays a significant role as a potential natural antibiotic for H. pylori clearance and a therapeutic agent for chronic gastritis.

Critical Role of Antimicrobial Peptide Cathelicidin for Controlling Helicobacter pylori Survival and Infection.

ATM is a 350 kDa serine/threonine kinase best known for its role in DNA repair and multiple cellular homeostasis pathways. Mutation in ATM causes the disease ataxia telangiectasia (A-T) with clinical features including ataxia, severe cerebellar atrophy and Purkinje cell loss. In a cross-species study, using primary rat neurons, the roundworm C. elegans, and a mouse model of A-T, we showed that loss of ATM induces mitochondrial dysfunction and compromised mitophagy due to NAD(+) insufficiency. Remarkably, NAD(+) repletion mitigates both the DNA repair defect and mitochondrial dysfunction in ATM-deficient neurons. In C. elegans, NAD(+) repletion can clear accumulated dysfunctional mitochondria through restoration of compromised mitophagy via upregulation of DCT-1. Thus, NAD(+) ties together DNA repair and mitophagy in neuroprotection and intimates immediate translational applications for A-T and related neurodegenerative DNA repair-deficient diseases.

NAD(+): The convergence of DNA repair and mitophagy.

Neurons affected in Alzheimer's disease (AD) experience mitochondrial dysfunction and a bioenergetic deficit that occurs early and promotes the disease-defining amyloid beta peptide (Aβ) and Tau pathologies. Emerging findings suggest that the autophagy/lysosome pathway that removes damaged mitochondria (mitophagy) is also compromised in AD, resulting in the accumulation of dysfunctional mitochondria. Results in animal and cellular models of AD and in patients with sporadic late-onset AD suggest that impaired mitophagy contributes to synaptic dysfunction and cognitive deficits by triggering Aβ and Tau accumulation through increases in oxidative damage and cellular energy deficits; these, in turn, impair mitophagy. Interventions that bolster mitochondrial health and/or stimulate mitophagy may therefore forestall the neurodegenerative process in AD.

Mitophagy and Alzheimer's Disease: Cellular and Molecular Mechanisms.

Mitochondrial dysfunction contributes to normal aging and a wide spectrum of age-related diseases, including neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. It is important to maintain a healthy mitochondrial population which is tightly regulated by proteolysis and mitophagy. Mitophagy is a specialized form of autophagy that regulates the turnover of damaged and dysfunctional mitochondria, organelles that function in producing energy for the cell in the form of ATP and regulating energy homeostasis. Mechanistic studies on mitophagy across species highlight a sophisticated and integrated cellular network that regulates the degradation of mitochondria. Strategies directed at maintaining a healthy mitophagy level in aged individuals might have beneficial effects. In this review, we provide an updated mechanistic overview of mitophagy pathways and discuss the role of reduced mitophagy in neurodegeneration. We also highlight potential translational applications of mitophagy-inducing compounds, such as NAD(+) precursors and urolithins.

Mitophagy in neurodegeneration and aging.

Aging is a major international concern that brings formidable socioeconomic and healthcare challenges. Small molecules capable of improving the health of older individuals are being explored. Small molecules that enhance cellular stress resistance are a promising avenue to alleviate declines seen in human aging. Tomatidine, a natural compound abundant in unripe tomatoes, inhibits age-related skeletal muscle atrophy in mice. Here we show that tomatidine extends lifespan and healthspan in C. elegans, an animal model of aging which shares many major longevity pathways with mammals. Tomatidine improves many C. elegans behaviors related to healthspan and muscle health, including increased pharyngeal pumping, swimming movement, and reduced percentage of severely damaged muscle cells. Microarray, imaging, and behavioral analyses reveal that tomatidine maintains mitochondrial homeostasis by modulating mitochondrial biogenesis and PINK-1/DCT-1-dependent mitophagy. Mechanistically, tomatidine induces mitochondrial hormesis by mildly inducing ROS production, which in turn activates the SKN-1/Nrf2 pathway and possibly other cellular antioxidant response pathways, followed by increased mitophagy. This mechanism occurs in C. elegans, primary rat neurons, and human cells. Our data suggest that tomatidine may delay some physiological aspects of aging, and points to new approaches for pharmacological interventions for diseases of aging.

Tomatidine enhances lifespan and healthspan in C. elegans through mitophagy induction via the SKN-1/Nrf2 pathway.

The coenzyme NAD(+) is critical in cellular bioenergetics and adaptive stress responses. Its depletion has emerged as a fundamental feature of aging that may predispose to a wide range of chronic diseases. Maintenance of NAD(+) levels is important for cells with high energy demands and for proficient neuronal function. NAD(+) depletion is detected in major neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases, cardiovascular disease and muscle atrophy. Emerging evidence suggests that NAD(+) decrements occur in various tissues during aging, and that physiological and pharmacological interventions bolstering cellular NAD(+) levels might retard aspects of aging and forestall some age-related diseases. Here, we discuss aspects of NAD(+) biosynthesis, together with putative mechanisms of NAD(+) action against aging, including recent preclinical and clinical trials.

Article	Year
A high-fat diet and NAD(+) activate Sirt1 to rescue premature aging in cockayne syndrome. Cell metabolism\| PubMed ID: 25440059	2014
Protecting the mitochondrial powerhouse. Trends in cell biology\| PubMed ID: 25499735	2015
Critical Role of Antimicrobial Peptide Cathelicidin for Controlling Helicobacter pylori Survival and Infection. Journal of immunology (Baltimore, Md. : 1950)\| PubMed ID: 26800870	2016
NAD(+): The convergence of DNA repair and mitophagy. Autophagy\| PubMed ID: 27929719	2017
Mitophagy and Alzheimer's Disease: Cellular and Molecular Mechanisms. Trends in neurosciences\| PubMed ID: 28190529	2017
Mitophagy in neurodegeneration and aging. Neurochemistry international\| PubMed ID: 28235551	2017
Tomatidine enhances lifespan and healthspan in C. elegans through mitophagy induction via the SKN-1/Nrf2 pathway. Scientific reports\| PubMed ID: 28397803	2017
NAD(+) in Aging: Molecular Mechanisms and Translational Implications. Trends in molecular medicine\| PubMed ID: 28899755	2017

Evandro F. Fang

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